In heat exchangers that utilize flattened tubes, it is known to provide header plates that have pierced tube receiving openings with flanges or collars surrounding the openings and conforming to the tube ends received in the openings so as to reduce the stress risers at the interfaces between the tubes and the header plate. It is also known for the flanges or collars to either extend into the fluid tank or manifold associated with the header plate or to extend away from (i.e., towards the core of the heat exchanger) the fluid tank or manifold associated with the header plate is attached. While the known designs may have proven adequate for their current applications, there is a continuous push to increase the design limits of heat exchanges in an effort to improve performance, compactness, life, etc., and because of this, there is a continuing need to improve the design of header plates and the associated heat exchangers.